1. Field of the Invention
The present invention relates to a transmitting apparatus, a transmitting method, a receiving apparatus, a receiving method, a transmitting and receiving system, and a transmitting and receiving method suitable for uni-directionally delivering hierarchical data that is distributed on a network.
2. Description of the Related Art
Many data delivering methods have been proposed. For example, http (Hyper Text Transfer Protocol) is used to publish pages on the Internet. TCP/IP (Transmission Control Protocol/Internet Protocol) enables computers connected to the Internet to exchange data. In the TCP/IP, a receiving side that receives data calls a transmitting side. Whenever data is transmitted or received corresponding to the TCP/IP, a connection is established between the receiving side and the transmitting side. Thus, with such protocols, data can be delivered with high reliability.
On the other hand, the transmitting side and the network are adversely overloaded and thereby data cannot be effectively delivered. In other words, when the number of terminal units that receive data is becoming large and they access a server that delivers data thereto at a time, the server and the network are adversely overloaded. Thus, even if a terminal unit requests the server for data, the terminal unit cannot receive the requested data from the server in a short time.
To solve such a problem, a method using a satellite line, a CATV (Cable Television) line, a ground wave digital broadcast, and so forth that allows data to be broadcast has been proposed. With this, method, even if the number of terminal units increases, the server and the network are prevented from being adversely overloaded.
In recent years, as digital communication networks such as the Internet have become common, a huge amount of data has been stored on the networks. Thus, it is desired to effectively use such data. To do that, a directory service for hierarchically managing data distributed on a network and providing the data to the user is becoming popular. Using the directory service, the user can quickly find desired information from data distributed on the network and access the desired information.
The directory service has been set forth as X.500 series in OSI (Open System Interconnection) that is an international standard. In the X.500, the directory is defined as a set of open systems. Individual open systems cooperatively have logical databases of information with respect to a set of objects of the real world.
With directory services defined in the X.500, the user can search and browse information stored in the directory. The directory services also provide the user with a list service (such as a telephone directory) and a user authenticating service. In the directory service, each object is assigned a unique name so that the user can easily memorize, infer, and recognize each object.
The directory services defined in the X.500 are very comprehensive. The program size of each directory service is very large. Thus, it is very difficult to accomplish a directory service on the Internet that uses the TCP/IP as a protocol. To solve such a problem, LDAP (Lightweight Directory Access Protocol) has been proposed as a compact type directory service for the TCP/IP.
When the user uses the directory service, he or she can filter the directory. A filtering mask with which the user filters the directory is designated corresponding to the user's tendencies and favorites against the directory. A filtering mask is designated to a particular information genre corresponding to a user's favorite. The user can selectively access directory information to which a filtering mask has been designated. The filtering process allows the user not to keep unnecessary information.
In recent years, a directory service using a broadcast data transmitting means such as a satellite line, a CATV line, a ground digital broadcast, or the like has been proposed. In this case, information is uni-directionally delivered with the directory service. Thus, the user cannot request the directory service for desired data. Consequently, in such a directory service, the same information is repeatedly transmitted.
The user side stores received information to an IRD (Integrated Receiver Decoder) or an STB (Set Top Box) that is a digital broadcast receiver connected to a television receiver. At this point, a filtering process is performed with the above-described filtering mask. Directory information corresponding to a user's favorite is selectively stored. A filtering mask used for the filtering process is designated on the user side.
When the hierarchical structure of the directory changes, the directory server side detects a substantial change of the directory and transmits update information that represents the detected change of the hierarchical structure to the user. At this point, when the user side processes the update information of all the hierarchical structure that has changed, the user side is overloaded. In particular, when the user side uses the STB or IRD, because of their insufficient process capabilities and storage capacities, the user side cannot properly process the update information.
Thus, when the user side processes only a hierarchical structure to which a filtering mask has been designated, the process amount of the user side can be reduced. However, in such a method, when the directory structure is dynamically varied, it will become meaningless to designate a filtering mask. Thus, the user cannot obtain his or her desired information.